Abstract: Synchronizer apparatus is provided in or for multi-section telescopic jibs comprising travel sensors each to be carried by a moveable jib section in at least one group of at least three sections, one of the sensors being adapted for interconnection with two travel sensors carried one by each of two other sections in the group for sensing disproportionate travel of one moveable section relative to travel of a further section with respect to another section, a signal device actuable by the sensors of each group and operative means for connecting the signal device to a power transmission valve associated with rams respectively operatively connected to the said one and said further moveable sections for controlling the travel of at least one of them to remove any disproportionate travel.